the secret is to have lots of suspension travel (maybe also another drive wheel on the front so that while your nose plows into the ground your still pulling yourself along) and to get the coconuts into the vehicle as fast as possible

I even tried reverse engineering (read:copying) mazda/nissan's cart and still nothing.

well the main problem with that cart is that the back flap gets caught up on the coconut chute, which slows you down about 1 second at the start. After that everything is full throttle to the saw blades